1. Field of the Invention
This invention relates to vehicle wheel alignment equipment, and more particularly, to a light beam projector for use in such equipment when obtaining orientation data for the wheels in a toe plane.
2. Description of the Prior Art
An aimable view finder for use in a wheel alignment system is disclosed in patent application U.S. Ser. No. 261,445, entitled INDIVIDUAL TOE MEASURING SYSTEM, filed of even date herewith. The disclosed view finder relates to an optical assembly wherein an objective lens is positioned at one end of a viewing path formed in a framework. A pair of plano prisms are mounted for rotation about the axis of the viewing path in a position on the image side of the objective lens so that light passed by the lens is intercepted and deflected in substantially equal and opposite vertical directions by the pair of plano prisms. Additional optics are provided through which the light emitted by the objective lens and skewed laterally by the plano prism pair may be viewed. A signal generator is coupled to the plano prisms so that a signal is provided which is indicative of the amount of lateral deflection imposed by the prisms on the light passed through the objective lens. An index line is provided in the optics to indicate on the observed image the direction in which the viewing path is aimed.
Apparatus providing rearward projecting light beams for use in determining the inclinations of front steerable wheels relative to the axis of rotation of one of the rear nonsteerable wheels are found in U.S. Pat. Nos. 4,154,531, Roberts, Jr. et al, issued May 15, 1979; 4,150,897, Roberts, Jr. et al, issued Apr. 24, 1979; 4,130,362, Lill et al, issued Dec. 19, 1978; and 4,097,157, Lill, issued June 27, 1978, all of which are currently assigned to the assignee of record of the invention disclosed herein.
The U.S. Pat. No. 4,154,531 patent discloses apparatus wherein the rearward projected beam is caused to swing through a predetermined angle. The beam is reflected by a mirror mounted in predetermined relationship with the axis of rotation of one of the rear nonsteerable wheels so that the oscillating beam is reflected back to a target mounted on the front steerable wheel on the same side of the vehicle. The time relationship between the instants when the projected oscillating beam is received by light sensitive devices when reflected toward the front wheel mounted target is used to determine the inclination of the front steerable wheel in the horizontal or toe plane.
A rotating prism is disclosed in the U.S. Pat. No. 4,150,897 specification which provides for linear displacement of the point of impingement of a beam on the surface of a lens to thereby cause the beam to transit through a sweep angle as it emerges from the projection side of the lens.
The U.S. Pat. No. 4,130,362 patent discloses a multiplicity of beams projected at known angles relative to a reference angle from a projector mounted on one of the steerable front wheels of the vehicle. A mirror mounted on the rear wheel on the same side of the vehicle in predetermined relationship with the axis of rotation of the rear wheel reflects one of the projected beams back to the front wheel assembly. The reflected and received beam from the multiplicity of beams determines the inclination of the front wheel in the horizontal or toe plane.
The U.S. Pat. No. 4,097,157 patent disclosure makes reference to a rearwardly projected beam which is reflected by a mirror mounted in predetermined relationship with a nonsteerable wheel on the same side of the vehicle. The reflected beam is received at an encoding target which is mounted on the front wheel on the same side of the vehicle to provide an indication of the inclination of the front wheel in a horizontal or toe plane relative to the axis of rotation of the rear wheel.